It is knwon that when spools of strand, especially glass strand are wound, it is essential that the outside surface of the spool be as homogeneous as possible and in particular, that the wound strand does not go beyond, even slightly, the ends of the spool, in order to avoid damage to the strand during later handling.
In order to make cylindrical spools, winding-machines have already been devised which include a forked thread to strand-guide which receives the strand to be wound from means such as bushing. The strand-guide is situated as near as possible to the winding spools, parallel to the axis of the spindle on which the spool is formed. The extent of the oscillatory motion corresponds approximately to the height of the spool to be formed, that is to say, to the length of its generator.
During spool formation, spool diameter increases progressively and it is therefore necessary to withdraw the thread-guide, and the unit on which it is movably mounted, away from the spindle for the strand in order to keep the same relative possition of the strand guide and the outer surface of the developing spool.
Winding-machines of this type have already been described in the following patents: U.S. Pat. Nos.: 3,367,587; 3,371,877; 3,498,550; 3,547,361; 3,717,311; 3,897,021; 3,801,032; 3,819,122; 3,838,827 and 3,845,912.
Among these patents, the most representative of the prior art is U.S. Pat. No. 3,547,361 in which a winding-machine is disclosed including a fixed frame on which a spindle or collet is rotatably mounted on which the strand is wound. This spindle or collet is connected to rotation means which also act on a strand-guide assembly to reciprocate the strand-guide, with the whole assembly being mounted for oscillation on the frame. The winding-machine also includes a driving means intended to cause rotation of the whole strand-guide in relation to the spindle, in accordance with the increase of the spool diameter during development. This drive means includes a regulating loop comprising a feeler for detecting the spool growth, and a drive means intended to rotate the arm and having an exciting unit responsive to the feeler position.
The feeler is preferably a roller which comes into contact with the spool when the strand-guide is placed immediately above the roller. The strand passes through the strand-guide then under the roller, after which it is wound on the spool.
The roller is fixed on an oscillating arm and is brought back towards the spool by a yieldable device formed of several pneumatic jacks. The oscillating arm can withdraw under the effect of the increase in spool size by means of an electric contact or a close-up detector which forms the excitation element and which acts when closed on the motor to move the oscillating arm away.
The disadvantage of the winding apparatus disclosed in U.S. Pat. No. 3,547,361 is especially the intermittent withdrawal motion of the oscillating arm in view of which the arm can move only by increments which cannot, from a practical point of view, be as small as desired.
The effect of incremental motion of the oscillating arm, which reflects itself on the thread-guide as well, is to produce periodically variable winding conditions. Depending on the case, the result is that the distance between the thread-guide and the spool cannot be as uniform as desired ad especially that the follower cannot exert a constant pressure on the spool or package.
While this effect may initially seem insignificant, in practice especially where glass strands are wound, the applicants have observed that the spools obtained show various defects because of the following imperfections.
The distance between the thread-guide and the roller follower is a factor which conditions the precision of the spool height (its generator length). If the precise accuracy is not rigorously the same the sides of the spool are irregular and concentric rings and corrugations can be observed which are composed of windings of thread more or less coming out of the body of the spool. A possibility of wear of these corrugations exists where ulterior manipulations occur in these particular places.
If the roller follower exerts an irregular pressure on the spool, the degradation of the strand follows these pressure changes. It results that the quality of the wound strand is not constant.
The lack of fidelity commonly recognized in making electric contact by the excitation element can produce irregular and relatively large increments of motion of the oscillating arm, that give slight variations on the spool in the wound length and irregularity in the spool sides as well. If the excitation element is formed by an electric microswitch contact, the follower must, in addition, overcome the resistance of this contact. This disturbs the application effort of the idler on the strand of the spool, which accentuates again its deterioration. The discontinuous efforts and the motion have the consequence that the resulting spool does not have a regular quality since at some time, the strand is exposed to a very low pressure.
In order that the roller follower is able to operate the excitation element formed by the electric micro-switch, it is necessary, since this roller follower belongs to equipment mounted for oscillation on the arm which itself is oscillating and which carries the thread-guide ad the micro-switch, that the spool surface exert a relatively large force on the follower on the order of 4 to 5 newtons, for example, in the case of the apparatus shown in U.S. Pat. No. 3,547,361.
To reduce this force, the equipment shown in this patent is provided with a system of jacks mounted between the mobile equipment of the follower and the oscillating arm. However, this system is relatively complicated and in any case very difficult to maintain because of the friction caused by the internal rubbing of the jacks.